Radioisotopes are source of particulate radiations (α, β-, β+) and electromagnetic radiations (γ and X-rays). These emissions are essential in modern healthcare and offer numerous industrial and societal applications. In healthcare, radioisotopes are used in both diagnostic imaging, through radiotracers, and therapeutic agents for treating cancer and tumors. Specifically, radioisotopes are placed in suitable carriers to target diseased cells (theranostics) or used in external radiotherapy. Additionally, high-energy γ-rays from sources like Co-60, Cs-137, or E-beams are standardly used for "cold" sterilization of packaged medical equipment, surgical consumables, blood, and delicate pharmaceutical products. This lecture explores approved radiation sources and radiopharmaceuticals, spanning imaging to theranostics. It will highlight ongoing research and the future, chemist-driven landscape of this field.